Currently the grub_diskfilter_memberlist() function returns all physical
volumes added to a volume group to which a logical volume (LV) belongs.
However, this is suboptimal as it doesn't fit the intended behavior of
returning underlying devices that make up the LV. To give a clear
picture, the result should be identical to running commands below to
display the logical volumes with underlying physical volumes in use.
localhost:~ # lvs -o lv_name,vg_name,devices /dev/system/root
LV VG Devices
root system /dev/vda2(512)
localhost:~ # lvdisplay --maps /dev/system/root
--- Logical volume ---
...
--- Segments ---
Logical extents 0 to 4604:
Type linear
Physical volume /dev/vda2
Physical extents 512 to 5116
As shown above, we can know system-root LV uses only /dev/vda2 to
allocate it's extents, or we can say that /dev/vda2 is the member device
comprising the system-root LV.
It is important to be precise on the member devices, because that helps
to avoid pulling in excessive dependency. Let's use an example to
demonstrate why it is needed.
localhost:~ # findmnt /
TARGET SOURCE FSTYPE OPTIONS
/ /dev/mapper/system-root ext4 rw,relatime
localhost:~ # pvs
PV VG Fmt Attr PSize PFree
/dev/mapper/data system lvm2 a-- 1020.00m 0
/dev/vda2 system lvm2 a-- 19.99g 0
localhost:~ # cryptsetup status /dev/mapper/data
/dev/mapper/data is active and is in use.
type: LUKS1
cipher: aes-xts-plain64
keysize: 512 bits
key location: dm-crypt
device: /dev/vdb
sector size: 512
offset: 4096 sectors
size: 2093056 sectors
mode: read/write
localhost:~ # vgs
VG #PV #LV #SN Attr VSize VFree
system 2 3 0 wz--n- 20.98g 0
localhost:~ # lvs -o lv_name,vg_name,devices
LV VG Devices
data system /dev/mapper/data(0)
root system /dev/vda2(512)
swap system /dev/vda2(0)
We can learn from above that /dev/mapper/data is an encrypted volume and
also gets assigned to volume group "system" as one of it's physical
volumes. And also it is not used by root device, /dev/mapper/system-root,
for allocating extents, so it shouldn't be taking part in the process of
setting up GRUB to access root device.
However, running grub-install reports error as volume group "system"
contains encrypted volume.
error: attempt to install to encrypted disk without cryptodisk
enabled. Set `GRUB_ENABLE_CRYPTODISK=y' in file `/etc/default/grub'.
Certainly we can enable GRUB_ENABLE_CRYPTODISK=y and move on, but that
is not always acceptable since the server may need to be booted unattended.
Additionally, typing passphrase for every system startup can be a big
hassle of which most users would like to avoid.
This patch solves the problem by returning exact physical volume, /dev/vda2,
rightly used by system-root from the example above, thus grub-install will
not error out because the excessive encrypted device to boot the root device
is not configured.
Signed-off-by: Michael Chang <mchang@suse.com>
Tested-by: Olav Reinert <seroton10@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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